Recently, somatotropin has been produced massively by using genetic engineering techniques. Bovine somatotropin has been commercialized to increase the productivity of milk and porcine somatotropin has been commercialized to improve feed conversion ratio and to improve meat quality and so on.
Most of bioactive somatotropin formulations developed until now are the sustained-releasing type that a large amount of somatotropin is administered and released slowly only to avoid the inconvenience of daily administration. For examples, U.S. Pat. No. 5,411,951 and U.S. Pat. No. 5,474,980 disclose the sustained-releasing composition produced by adding a gelling agent such as aluminum monostearate into vegetable oil, and by gelatinizing oil by heating, and by mixing somatotropin homogeneously. These techniques have been already used to prepare sustained-releasing composition of antibiotics (U.S. Pat. No. 2,491,537, U.S. Pat. No. 2,507,193, U.S. Pat. No. 3,016,330), pamoate salts of oxazepin (U.S. Pat. No. 3,676,557) or relaxin (U.S. Pat. No. 2,964,448), parathyroid stimulating hormone (U.S. Pat. No. 3,869,549), luteinizing hormone releasing factor (U.S. Pat. No. 4,256,737), gonadotropin (U.S. Pat. No. 3,852,422) and insulin (U.S. Pat. No. 2,143,590, U.S. Pat. No. 2,174,862, U.S. Pat. No. 2,920,014, U.S. Pat. No. 3,102,077) and the like.
There are similar techniques for preparing sustained-releasing type by using oil. For example, EP 211691 discloses that somatotropin is mixed with wax and oil complex and EP 213851 suggests that sustained-releasing formulation is prepared by mixing somatotropin with oil and glyceride release-modifying agent available commercially. And EP 314421 discloses that sustained-releasing somatotropin composition is prepared by adding absorption-controlling material such as calcium stearate and dextran to oil. But this is a formulation that active ingredient has been substituted with somatotropin in the known oil-injection formulation.
In addition, the sustained-releasing techniques without using oil have been attempted. For example in EP 193917 somatotropin was mixed with water-soluble polysaccharides such as starch and dextrin to improve the sustained-releasing effect. But this formulation has shorter releasing time than other formulations mixed with oil and the somatotropin is unstable with water-soluble ingredients.
Another technique which does not use oil to prolong the releasing time has been described in U.S. Pat. No. 5,520,927. It discloses the formulation of tocopherol acetate and a release-delaying agent. However, in this case tocopherol acetate is used only for delaying the release of drug.
Different techniques from the above-mentioned have been attempted for sustained-releasing somatotropin formulations. U.S. Pat. No. 4,861,580 discloses sustained-releasing somatotropin formulation is prepared as a liposome type by using lipid-soluble material such as phosphatidyl choline, phosphatidyl ethanolamine and alpha-tocopherol hemisuccinate tris salt. And in U.S. Pat. No. 4,675,189 sustained-releasing somatotropin formulation was prepared as a microcapsule type by using bio-compatible polymer. And in U.S. Pat. No. 4,857,506 sustained-releasing somatotropin formulation is prepared as a multiple water-in oil-in water emulsion. But these are inadequate to be commercialized since the processes are so complex and high technologies are required. Furthermorer the recovery rate to produce the desirable somatotropin is too low to be commercialized. In addition the somatotropin formulations prepared by the process are not stable and can not show the desirable sustained-release effect.
By using quite different methods, solid formulations which are implantable were prepared for improving the sustained-release of drugs. These techniques have been described in U.S. Pat. No. 4,452,775, U.S. Pat. No. 4,761,289, U.S. Pat. No. 4,765,980, U.S. Pat. No. 4,786,501, U.S. Pat. No. 4,863,736, U.S. Pat. No. 5,035,891, U.S. Pat. No. 5,198,422, U.S. Pat. No. 5,228,697, U.S. Pat. No. 5,356,635, U.S. Pat. No. 5,595,752 and EP 246540, 462959, PCT/US92/01877, PCT/US91/08129, PCT/US90/01340, PCT/AU87/00139 and the like. In these techniques solid somatotropin compositions were prepared and implanted into the animal body by surgical operation or by using special instruments which are expensive. The implanting techniques make it possible to release the desirable amount of bioactive somatotropin during the desirable period. However, the implanting process is too difficult to be performed and animals also feel uncomfortable due to the foreign substance.
The inventors of the present invention have conducted the intensive research for the sustained-release formulation of somatotropin to solve the above-mentioned problems. The inventors have found that somatotropin mixed with lipid-soluble vitamins at proper proportions shows the excellent sustained-release effect and additionally the synergic effect of the active ingredients by administering parenterally.